Electron Gun Diaphragm Layout for NEA Surface Protection
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Solution Overview
Problem
The electron beam emitted from a photoelectric film with a negative electron affinity (NEA) surface deteriorates due to gas molecules entering the electron gun chamber, leading to reduced luminance characteristics and instability of the emission current, especially in low vacuum environments.
Innovation Solution
An electron microscope design with a non-axisymmetric first differential exhaust diaphragm and a deflector to control the electron beam trajectory, preventing gas molecules from reaching the photoelectric film while maintaining high luminance and stability, allowing operation in low vacuum conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multi-stage differential exhaust structure with axisymmetric diaphragms is used to maintain high vacuum, then the electron beam can be properly transmitted, but gas molecules can still reach the photoelectric film through the axisymmetric passage holes, causing NEA surface deterioration
Solution Approach 1:
The first differential exhaust diaphragm is designed with a non-axisymmetric passage hole configuration. Specifically, the passage holes are positioned at asymmetric locations relative to the electron optical axis, creating an asymmetric vacuum barrier that effectively blocks gas molecule flow paths while allowing electron beam transmission. This asymmetric design prevents gas molecules from reaching the photoelectric film surface, thereby protecting the NEA surface from deterioration and extending its operational life.
2Device complexity
If the electron beam passes through axisymmetric diaphragm holes, then the trajectory can be simplified, but gas molecules flow directly from the sample chamber to the electron gun chamber, deteriorating the NEA surface
Solution Approach 1:
The first differential exhaust diaphragm employs non-axisymmetric passage hole positioning to create an asymmetric gas flow barrier. This design disrupts the direct gas flow path from the sample chamber to the electron gun chamber, preventing gas molecules from reaching the photoelectric film. The asymmetric configuration maintains effective vacuum isolation while still allowing electron beam transmission through the diaphragm.
3Illumination intensity
If high emission current is used to improve observation performance, then the luminance characteristics are enhanced, but ion feedback increases causing faster NEA surface deterioration
Solution Approach 1:
The non-axisymmetric passage hole design in the first differential exhaust diaphragm creates effective vacuum isolation that reduces gas molecule presence in the electron gun chamber. This vacuum protection minimizes ion feedback events even during high emission current operation, thereby protecting the NEA surface from rapid deterioration while allowing high luminance characteristics to be maintained.
4Ease of manufacture
If axisymmetric diaphragm holes are used, then the structure is simpler and alignment is easier, but gas molecules can pass through unshielded, reducing vacuum quality
Solution Approach 1:
The first differential exhaust diaphragm is designed with non-axisymmetric passage hole positions to create an asymmetric vacuum barrier. This asymmetric configuration effectively blocks gas molecule flow paths from the sample chamber to the electron gun chamber, maintaining high vacuum quality in the electron gun chamber while still allowing electron beam transmission through the diaphragm structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents gas molecule adsorption and ion feedback, stabilizes the emission current, and extends the life of the NEA surface, enabling high spatial resolution and luminance characteristics in low vacuum environments.
Implementation Method 1
a photoelectric film (photocathode) formed on a transparent substrate... an electron beam generated from the photoelectric film when the excitation light condensed by the condensing lens is incident through the transparent substrate of the photoelectric film
Implementation Method 2
a condensing lens configured to condense the excitation light toward the photoelectric film
Implementation Method 3
an anode electrode provided facing the photoelectric film and configured to accelerate an electron beam
Data Source
AI summary
In an axisymmetric electron gun structure, a part of gas molecules flowing from a vacuum chamber having relatively low vacuum reach a photoelectric film, causing problems of deterioration of an NEA surface, instability of an emission current, and a reduction in life of the photoelectric film. An electron microscope including an excitation light source; a photoelectric film formed on a transparent substrate; a condensing lens configured to condense excitation light to the photoelectric film; an anode electrode configured to accelerate an electron beam that is generated when the excitation light is condensed and irradiated to the photoelectric film; a first differential exhaust diaphragm provided close to the photoelectric film and having a passage hole off an axis; a second differential exhaust diaphragm provided close to a sample and having a passage hole on an optical axis; and a deflector for trajectory control of the electron beam.